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Karst aquifers contribute substantially to freshwater supplies in many regions of the world, but are vulnerable to contamination and difficult to manage because of their unique hydrogeological characteristics. Many karst systems are hydraulically connected over wide areas and require transboundary exploration, protection and management. In order to obtain a better global overview of karst aquifers, to create a basis for sustainable international water-resources management, and to increase the awareness in the public and among decision makers, the World Karst Aquifer Mapping (WOKAM) project was established. The goal is to create a world map and database of karst aquifers, as a further development of earlier maps. This paper presents the basic concepts and the detailed mapping procedure, using France as an example to illustrate the step-by-step workflow, which includes generalization, differentiation of continuous and discontinuous carbonate and evaporite rock areas, and the identification of non-exposed karst aquifers. The map also shows selected caves and karst springs, which are collected in an associated global database. The draft karst aquifer map of Europe shows that 21.6% of the European land surface is characterized by the presence of (continuous or discontinuous) carbonate rocks; about 13.8% of the land surface is carbonate rock outcrop.

Periodic quality assessment of drinking water sources is necessary to guarantee the quality and security of water supply to people. Accordingly, this study assessed the drinking water quality of spring water of some villages located in Barwari Bala region of Duhok Governorate, Kurdistan region, Iraq, using the water quality index (WQI). To realize this objective, 120 spring water samples were collected from ten villages during the dry and wet seasons in 2018 and were analyzed for major physicochemical characteristics, including: calcium (Ca2+), magnesium (Mg2+), sodium (Na+), potassium (K+), chloride (Cl−), sulfate (SO42−), nitrate (NO3−), pH, total dissolved solids (TDS), turbidity, total hardness (TH) and total alkalinity (TA). The results for pH, turbidity, sodium, potassium, chloride, sulfate and nitrate showed that the water samples at all the sampled springs were suitable for drinking and within permissible limits based on given standards. However, TDS, TA, calcium and magnesium exceeded the permissible limits at some sites. It was also observed that, except for SO42−, at almost all the sites, the majority of parameters were significantly greater during the wet season compared to the dry season. With reference to all the parameters, the WQI values ranged from 10.76 to 18.13 during the dry season and from 17.10 to 20.45 during the wet season, indicating that all water samples are classified as having “excellent” water quality for drinking purposes. The calculation of WQI based on specific parameters, where values were close to or exceeded the maximum acceptable limits, showed that the water quality status of all water samples was “good” quality, except for sites S6 and S8, which were classified as “poor” quality and are not considered suitable for drinking purposes without treatment. Water from almost all the sampled spring sites can be considered as suitable for drinking purposes, although some parameters exceed permissible limits. Simple filtration treatment of the sampled spring water before use is desirable for ensuring good quality and security of the water supply to people of these areas.

Karst springs are essential drinking water resources, however, modeling them poses challenges due to complex subsurface flow processes. Deep learning models can capture complex relationships due to their ability to learn non‐linear patterns. This study evaluates the performance of the Transformer in forecasting spring discharges for up to 4 days. We compare it to the Long Short‐Term Memory (LSTM) Neural Network and a common baseline model on a well‐studied Austrian karst spring (LKAS2) with an extensive hourly database. We evaluated the models for two further karst springs with diverse discharge characteristics for comparing the performances based on four metrics. In the discharge‐based scenario, the Transformer performed significantly better than the LSTM for the spring with the longest response times (9% mean difference across metrics), while it performed poorer for the spring with the shortest response time (4% difference). Moreover, the Transformer better predicted the shape of the discharge during snowmelt. Both models performed well across all lead times and springs with 0.64–0.92 for the Nash–Sutcliffe efficiency and 10.8%–28.7% for the symmetric mean absolute percentage error for the LKAS2 spring. The temporal information, rainfall and electrical conductivity were the controlling input variables for the non‐discharge based scenario. The uncertainty analysis revealed that the prediction intervals are smallest in winter and autumn and highest during snowmelt. Our results thus suggest that the Transformer is a promising model to support the drinking water ion management, and can have advantages due to its attention mechanism particularly for longer response times. Key Points The Transformer architecture was applied in karst hydrology for the first time, showing high performance for discharge forecasting Monte Carlo dropout revealed that the prediction intervals are smallest and cover the measured discharges best in winter and autumn The high temporal resolution of the input data sets improved the forecasting performance

Climate change is projected to threaten groundwater resources in many regions, but projections are highly uncertain. Quantifying the historic impact potentially allows for understanding of hydrologic changes and increases confidence in the predictions. In this study, the responses of karst discharge to historic and future climatic changes are quantified at Blautopf Spring in southern Germany, which is one of the largest karst springs in central Europe and belongs to a regional aquifer system relevant to the freshwater supply of millions of people. Statistical approaches are first adopted to quantify the hydrodynamic characteristics of the karst system and to analyse the historic time series (1952–2021) of climate variables and discharge. A reservoir model is then calibrated and evaluated with the observed discharge and used to simulate changes with three future climate-change scenarios. Results show that changes in the annual mean and annual low discharge were not significant, but the annual peak discharge shifted to a low state (<13.6 m3 s−1) from 1988 onwards due to decreasing precipitation, increasing air temperature, and less intense peak snowmelt. The peak discharge may decrease by 50% in this century according to the projections of all climate-change scenarios. Despite there being no significant historic changes, the base flow is projected to decrease by 35–55% by 2100 due to increasing evapotranspiration. These findings show the prolonged impact of climate change and variability on the floods and droughts at the springs in central Europe, and may imply water scarcity risks at similar climatic and geologic settings worldwide.

Karst water are important for water supply and ecological protection. However, climate changes and human activities have caused severe water supply crisis. The Jinci spring, one of the famous karst springs in China, is located at the basin‐mountain coupling belt and dried up since 1994. This study integrated hydrogeological conditions, water table logs, hydrogeochemistry, multiple isotopes, and numerical modeling to understand dynamic changes of interaction pattern between karst water‐Quaternary groundwater response to human activity in the basin‐mountain coupling belt over the past 60 years. Our investigation indicated that under natural conditions (1960s), karst water discharges as springs and laterally recharges into Quaternary groundwater at the fault area. In the 1980s, overexploitation caused a significant reduction in spring discharge and a decline in karst water levels, especially in coal mining areas. Further declines in water levels and mixing recharge by karst water‐Quaternary groundwater were observed in the 2000s, which were eased in 2018. Calculations both by oxygen isotope and models indicated that contribution of Quaternary groundwater to Jinci spring ranged from 11.8% to 42.1%, with the highest in the 2000s. Evidenced by multiple isotopes, the recharging of karst water‐Quaternary groundwater varied spatially along the belt in 2018, with delayed water level elevation in coal mining and heavy groundwater exploration areas. This study demonstrated that artificial disturbance fundamentally affected the karst water‐Quaternary groundwater flow and water exchange between them. Precautions should be taken when evaluating global water resources changes, in view of the dynamic interaction between the karst water‐Quaternary groundwater spatially and temporally. Plain Language Summary Global changes and human activities have changed groundwater flow and cycle, which is more pronounced in basin‐mountain coupling belt. However, how human activity influences the groundwater dynamics is unknown. The Jinci spring, one of the famous karst springs located at basin‐mountain coupling belt, was selected as a study area to address this knowledge gap. Based on the hydrogeological investigation, multiple isotopes and numerical modeling, we demonstrated the dynamic interaction of the karst water‐Quaternary groundwater and the potential impact of human activity along basin‐mountain coupling belt over the past decades. The interaction between the karst water‐Quaternary groundwater has changed in time and space. Under natural conditions in 1960s, karst water laterally flows into the Quaternary water. However, in 1980s, water level declines, and thus a part of Quaternary groundwater recharge into the karst water, which was even worse in 2000s. In 2018, water level rises, with a delay elevation in coal mining and heavy groundwater exploration areas. Over the past decades, Quaternary groundwater contributes to Jinci spring with varying ratios (11.8%–42.1%, with the highest in 2000s). Our findings emphasize that precautions should be taken when evaluating global water resources changes, considering the dynamic interaction between the karst‐Quaternary groundwater spatially and temporally. Key Points Hydrodynamic field and interaction between karst water‐Quaternary water have changed in spatial and temporal scales Human activity have fundamentally affected the natural groundwater evolution Precautions are required for the evaluation of global water resources changes

Karst groundwater resources in the Zagros Mountains are vital for supplying different demands in the region which need sustainable management and protection. Quantitative and qualitative characterization of karst aquifers in this region was understudied due to a lack of site-specific logging data and speleological investigations. In this study, state-of-the-art statistical methods developed to characterize karst aquifer based on analyses of the spring recession hydrograph and spring water quality are presented. These methods include Mangin’s method for the classification of karst aquifers, relationships of precipitation and discharge data, groundwater quality index (GQI), hydrochemical diagrams (Piper, Durov, and Gibbs), and calcite and dolomite saturation indices, Chloro-Alkaline indices (CAI), and 10 bivariate plots of hydrochemistry of spring waters. 42 major karst springs mainly located in folded part of the Zagros region (western Iran) are selected for application of the reviewed methods. Results indicated that the saturated zone exerts almost the main control over the discharge of 76% of the studied springs. The base-flow contributes between 80.0 and 100% of total water storage in the study aquifers. 78.5% of the studied aquifers have a high karstification degree. An insignificant lag time is observed between the precipitation on the karst basin and spring discharge. The hydrochemical diagrams show that the waters are dominated by HCO3 and Ca and the majority of the waters are alkaline, originating from carbonate rocks–water interaction through the ion exchange process. Moreover, the water sources of the studied springs are young and feed through precipitation (during the rainy season) and drainage from the upper karst setting (during the dry season). Such repeatable methods adopted in this study can provide crucial information for the karst aquifers, especially those suffering from scarcity of aquifer hydrodynamic data.

Comprehensive management of karst water resources requires sufficient understanding of their dynamics and karst-specific modeling tools. However, the limited availability of observations of karstic groundwater dynamics has been prohibiting the assessment of karst water resources at regional to global scales. This paper presents the first global effort to integrate experimental approaches and large-scale modeling. Using a global soil-moisture monitoring program and a global database of karst spring discharges, the simulations of a preliminary global karstic-groundwater-recharge model are evaluated. It is shown that soil moisture is a crucial variable that better distinguishes recharge dynamics in different climates and for different land cover types. The newly developed dataset of karst spring discharges provides first insights into the wide variability of discharge volumes and recharge areas of different karst springs around the globe. Comparing the model simulations with the newly collected soil-moisture and spring-discharge observations, indicates that (1) improvements of the recharge model are still necessary to obtain a better representation of different land cover types and snow processes, and (2) there is a need to incorporate groundwater dynamics. Applying and strictly evaluating these improvements in the model will finally provide a tool to identify hot spots of current or future water scarcity in the karst regions around the globe, thus supporting national and international water governance.

The Thulokhola watershed of the Nuwakot district in the midhills region of Nepal can be considered typical of climate change-related stresses in the region. To assess the status of water resources and document farmers' perceptions of and adaptation to climate change impacts in this watershed, we invited community groups to monitor water quality and conducted 6 focus group meetings, 3 participatory rural appraisals, and spring and household surveys in 2011 and 2012. Historical precipitation data from a nearby weather station and discharge data for the Tadi Khola, the nearest major river, were also analyzed. The spring survey results confirmed farmers' perceptions and showed that 73.2% of the springs used as water sources had a decreased flow and 12.2% had dried up over the past 10 or more years, as recognized by local residents. In response to the severe decline of precipitation and the drying up of springs, local communities have implemented some climate change adaptation measures, such as constructing water tanks at water sources, using pipes to transport drinking water, diverting water from other springs, digging deeper wells, and traveling farther to wash clothes and fetch drinking water. To enhance drinking water supplies and ensure the agricultural, ecological, and environmental integrity of the watershed, initiatives such as comprehensive research on springs and groundwater hydrology, a spring rejuvenation program, and community capacity building for water sustainability and climate change adaptation are suggested.

Background Water is the most abundant resource on earth, however water scarcity affects more than 40% of people worldwide. Access to safe drinking water is a basic human right and is a United Nations Sustainable Development Goal (SDG) 6. Globally, waterborne diseases such as cholera are responsible for over two million deaths annually. Cholera is a major cause of ill-health in Africa and Uganda. This study aimed to determine the physicochemical characteristics of the surface and spring water in cholera endemic communities of Uganda in order to promote access to safe drinking water. Methods A longitudinal study was carried out between February 2015 and January 2016 in cholera prone communities of Uganda. Surface and spring water used for domestic purposes including drinking from 27 sites (lakes, rivers, irrigation canal, springs and ponds) were tested monthly to determine the vital physicochemical parameters, namely pH, temperature, dissolved oxygen, conductivity and turbidity. Results Overall, 318 water samples were tested. Twenty-six percent (36/135) of the tested samples had mean test results that were outside the World Health Organization (WHO) recommended drinking water range. All sites (100%, 27/27) had mean water turbidity values greater than the WHO drinking water recommended standards and the temperature of above 17 °C. In addition, 27% (3/11) of the lake sites and 2/5 of the ponds had pH and dissolved oxygen respectively outside the WHO recommended range of 6.5–8.5 for pH and less than 5 mg/L for dissolved oxygen. These physicochemical conditions were ideal for survival of Vibrio. cholerae . Conclusions This study showed that surface water and springs in the study area were unsafe for drinking and had favourable physicochemical parameters for propagation of waterborne diseases including cholera. Therefore, for Uganda to attain the SDG 6 targets and to eliminate cholera by 2030, more efforts are needed to promote access to safe drinking water. Also, since this study only established the vital water physicochemical parameters, further studies are recommended to determine the other water physicochemical parameters such as the nitrates and copper. Studies are also needed to establish the causal-effect relationship between V. cholerae and the physicochemical parameters.

Atmospheric precipitation is the main source of replenishment for large karst springs in the northern China. The extensive spring area and the high heterogeneity and anisotropy of the karst aquifer can cause a significant lag in the response of spring water level to precipitation. To explore the response characteristics of different flows of groundwater to precipitation, this study took the Jinan spring area as an example and used time series analysis to investigate the response characteristics of spring to rainfall. This study showed that atmospheric precipitation remains the single most important factor affecting spring discharge at present. According to the characteristics of spring discharge recession, the groundwater flows in the Jinan spring area can be divided into conduit-major fissure flow and diffuse-minor fissure flow. This study examined the response characteristics of different groundwater flows to precipitation through correlation and spectral analyses. The response time of conduit-major fissure flow to precipitation ranged 7–16 days and the duration ranged 12–24 days. The response time of diffuse-minor fissure flow to precipitation ranged 36–56 days, and the duration ranged 1–3 hydrological years. Compared with the karst water system in the southern China, the karst water system in the northern China has a stronger regulating effect. On this basis, this study proposed a correlation and spectral analyses and evaluation method suitable for understanding the dynamics of large karst springs in the northern China.